KR20110022054A - Coatings - Google Patents

Abstract

Superhydrophilic coatings can be antireflective and antifog. The coating can maintain antireflection and antifogging for an extended period of time. The coating can have a graded refractive index. Wafer-level optics coatings may be for capillary condensation targeted at nanoparticles, including reflow-compatible coatings.

Description

Coating {COATINGS}

A claim of priority

This application claims the priority of US Provisional Application No. 61 / 061,806 filed June 16, 2008 and US Patent Application No. 12 / 473,803 filed May 28, 2009, both of which are incorporated in their entirety. Are incorporated by citation.

Federally-funded research or development

The present invention is granted by Grant No., awarded by NSF. Under the DMR-0213282, the Treasury assistance was made. The government has certain rights in the invention.

Technical Field

The present invention relates to a coating.

Multiple layers of nanoparticles and / or polymer electrolytes can be readily assembled to various surfaces. The choice of materials, assembly conditions, and post-processing conditions can be used to control the chemical, structural and optical properties of the final product.

Nanoparticles and polymers can be combined into conformal, graded-index, organic-inorganic composite antireflective coatings with significant optical performance on glass and epoxy substrates using interlayer (LbL) assemblies. The refractive index grade can be improved by absorbing (and incorporating) the material differently in the nanopore as a function of the effective capillary radius. A stable antireflective (AR) coating can be formed from an interlayer assembled film comprising nanoparticles and a polyelectrolyte.

In one aspect, the surface comprises a nanoporous coating comprising a first thickness having a first porosity and a second thickness having a second pore different from the first pore.

The first thickness may comprise a first plurality of nanoparticles having a first diameter. The second thickness may include a second plurality of nanoparticles having a second diameter different from the first diameter. The coating can have a thickness of less than 500 nm, or less than 300 nm. The surface may be transparent.

The surface may comprise a first functionalizing compound present in the first pore as capillary condensation. The first functionalized compound can be substantially free from the second pores. The surface may comprise a second functionalized compound present in the second pore as capillary condensation. The first and second functional compounds may be different.

In another aspect, a method of coating a surface includes positioning a first plurality of nanoparticles having a first diameter on a substrate, and a second plurality of nanoparticles having a second diameter different from the first diameter. Positioning in the

The method may include exposing the first plurality of nanoparticles to the first functional moiety. The method may include exposing a second plurality of nanoparticles to a second functional moiety. The first and second functional moieties may be different.

In another aspect, a method of coating a surface includes positioning a first material of a first thickness having a first refractive index on a substrate, and placing a second material of a second thickness having a second refractive index on the substrate, and Exposing the first material and the second material to a functional moiety.

The method may include selecting a first material comprising a plurality of nanoparticles having a first size. The first size may be selected based on the desired first refractive index. This method can select a second material comprising a plurality of nanoparticles having a second size. The second size can be selected based on the desired second refractive index.

In another method, the method of coating the surface comprises the steps of selecting a first plurality of nanoparticles capable of forming capillary pores having a first desired capillary radius r _C1 ; Forming a coating on the substrate, wherein the coating comprises a first plurality of nanoparticles; And exposing the coating to a vapor of a functionalized compound capable of forming capillary condensation in a capillary cavity having a first desired capillary radius r _C1 .

The method may include selecting a functionalized compound capable of forming capillary condensation in capillary pores having a first desired capillary radius r _C1 .

The method may include selecting a second plurality of nanoparticles capable of forming capillary pores having a second desired capillary radius r _C2 . The first plurality of nanoparticles, the second plurality of nanoparticles, and the functionalized compound may form capillary condensation in the capillary pores where the functionalized compound has a first desired capillary radius r _C1 , but a second desired It may be selected such that capillary condensation cannot be substantially formed in capillary pores having a capillary radius r _C2 .

In another aspect, the surface comprises a nanopore coating comprising a preselected pore and a preselected functionalized compound, wherein the functionalized compound is capillary-condensed within the pore.

The nanopore coating may comprise a plurality of inorganic nanoparticles having capillary pores in the nanoparticles. The functionalized compound may be a polymer or a polymer precursor.

In particular, the coating can be prepared by bringing liquid condensation into the selected capillary space within the coating. Condensation forms only in small capillary spaces and does not fill all possible pore spaces. The liquid is introduced to the coating by exposing the coating to the vapor of the liquid. Contacting the liquid with the coating by absorption or infiltration does not form capillary condensation. The vapor can penetrate the pore space of the coating and condense to the desired capillary space. The location of condensation in the coating is controlled by selecting the material and the properties of the coating.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

1 is a schematic depiction of a surface coating.
FIG. 2 is a graph showing permeability and thickness measurements for films with different numbers of bilayers.
3A and 3B are graphs showing transmittance and reflectance spectra for glass slides coated with a polymer electrolyte multilayer.
4 is a graph showing simulation of an optimal single-layer antireflective coating on a substrate having a refractive index of n-1.49.
5 is a schematic diagram illustrating how capillaries are formed at the junction of nanoparticles.
FIG. 6 is a graph showing the percentage increase in refractive index of nanoparticle coatings (consisting of various particle sizes) upon penetration into water and PDMS (via capillary condensation).
7 is a schematic diagram showing different capillary condensation in different areas of a coating with different size nanoparticles.
8A and 8B are graphs showing reflectance curves for coatings with a two-stack design after infiltration with water (FIG. 8A) and PDMS (FIG. 8B). Optical properties of the structure as assembled (non-penetrating, non-functionalized) are also provided by reference.
FIG. 9 is a graph showing PDMS-penetrated, two-stack AR film before and after aging in a humidity chamber (37 ° C., 80% rh) for 60 hours.
10A-1OB are graphs showing the optical properties of PDMS-penetrated two-stack AR films before and after extended heating at 85 ° C., where the overall film thickness measured using spectroscopic ellipsometric measurements is ˜150 nm (FIG. 10a) and ˜120 nm (FIG. 10b).
11 is a graph comparing the optical properties of assembled, PDMS-infiltrated, and PEGDMA-infiltrated two-stack AR films.
12A-12B are graphs showing the optical properties of PDMS- and TEGDMA-infiltrated two-stack AR films before and after heating at 85 ° C. for 22 hours and 44 hours, where any significant between 22 and 44 hours No change occurred (indicating that a new thermodynamic equilibrium was reached).
FIG. 13 shows the change (or lack) in the optical properties of TEGDMA-penetrated and subsequently UV-crosslinked two-stack AR films upon prolonged heating at 85 ° C. (22 and 44 hours). As a graph, it demonstrates that infiltrated functional chemicals can be further reacted with phosphorus drilling.

Many surfaces, often transparent surfaces, benefit from the presence of antireflective coatings. Preferably, the coating is robust, thin and optically transparent. For manufacturing purposes, the coating preferably does not require complicated equipment, can be quickly assembled to a variety of materials, and is conformally formed on the composite surface. In some embodiments, the coating can be antifogging and antireflective. In some circumstances, the coating may be hydrophilic, hydrophobic, superhydrophilic, or superhydrophobic.

The antireflective coating can be a thin coating having a graded refractive index profile. In other words, the coating can have a refractive index that varies as a function of thickness. The graded refractive index profile can provide a gradual transition in refractive index from one medium (eg, the refractive index of the substrate supporting the coating) to the other medium (eg, the refractive index of air). The refractive index profile can be smooth or stepwise. The refractive index (eg, at different points across the thickness of the coating) at different regions of the coating can be determined, for example, by adjusting the pores of the pore layer, by functionalizing one or more layers, or by Can be adjusted by combination.

Surfaces with nanotextures can exhibit extreme wetting properties. Nanotextured refers to surface properties such as ridges, valleys or pores that have nanometer (ie typically less than 1 micrometer) dimensions. In some cases, although some individual properties may exceed 1 micrometer in size, they will have average or rms dimensions on the nanometer scale. The nanotexture can be a 3D network of correlated or separated pores. Depending on the structure and chemical composition of the surface, the surface may be hydrophilic, hydrophobic, or extremely hydrophilic or superhydrophobic. One method for producing the desired textures involves multiple layers of polyelectrolyte. The polymer electrolyte multilayer can also impart desirable optical properties such as reflectivity, or antireflection, to the surface in a desired range of wavelengths. See, eg, US Patent Application Publication Nos. 2003/0215626, and 2006/0029634, each of which is incorporated by reference in its entirety.

Textured surfaces can promote extreme wetting behavior. Early theoretical studies by Wenzel and Cassie-Baxter and more recent studies by Quere and coworkers suggest that it is possible to significantly improve surface wetting with water by introducing roughness at the correct length scale. For example, Wenzel, RN J. Phys. Colloid Chem. 1949, 53, 1466; Wenzel, RN Ind. Eng. Chem. 1936, 28, 988; Cassie, ABD; Baxter, S. Trans. Faraday Soc. 1944, 40, 546; Bico, J .; Et al., D. Europhysics Letters 2001, 55, (2), 214-220; And Bico, J .; See Europhysics Letters 1999, 47, (6), 743-744, etc., each of which is incorporated by reference in its entirety. Based on these studies, it has recently been demonstrated that both lithographically textured surfaces and microporous surfaces can be superhydrophilic. For example, McHale, G .; Shirtcliffe, NJ; Aqil, S .; Perry, C. C; See Newton, MI Physical Review Letters 2004, 93, (3), which are incorporated by reference in their entirety. Interesting possibilities to switch between superhydrophobic and superhydrophilic states have been demonstrated as part of these surface structures. For example, Sun, TL; Angewandte Chemie-International Edition 2004, 43, (3), 357-360; Gao, YF; Langmuir 2004, 20, (8), 3188-3194; And US Patent Application Publication Nos. 2006/0029808, 2007/0104922, and 2008/0038458, each of which is incorporated by reference in its entirety.

The interlaminar treatment of multiple layers of polymer electrolyte can be used to make conformal thin film coatings by controlling film thickness and molecular level for the compound. The charged polyelectrolyte may be assembled in an interlayer manner. In other words, positively- and negatively-charged polyelectrolytes may alternatively be deposited on a substrate. One method of positioning the polyelectrolyte may include depositing the polyelectrolyte by contacting the substrate with an aqueous solution of the polyelectrolyte at an appropriate pH. The pH may be selected such that the polyelectrolyte is partially or weakly charged. The multiple layers can be described by the number of bilayers it contains, which leads to sequential application of the oppositely charged polyelectrolyte. For example, a plurality of layers having the order of layers PAH-PAA-PAH-PAA-PAH-PAA can be said to be made of three bilayers.

Three methods can provide a new level of molecular control over the deposition process by simply adjusting the pH of the treatment solution. The non-porous polymer electrolyte multilayer may form a thin film structure of pores induced by a simple acidic, aqueous process. Tuning of such pore forming processes, for example by manipulation of parameters such as salt content (ion strength), temperature, or surfactant chemistry, can result in the production of micropores, nanopores, or combinations thereof. Nanopores have a diameter of less than 150 nm, for example 1 to 120 nm or 10 to 100 nm. Nanopores can have a diameter of less than 100 nm. Micropores have a diameter over 150 nm and typically have a diameter over 200 nm. The selection of pore forming conditions can provide control over the pores of the coating. For example, the coating can be a nanopore coating, substantially free of micropores. Alternatively, the coating can be a microporous coating having an average pore diameter above 200 nm, such as, for example, 250 nm, 500 nm, 1 micron, 2 microns, 5 microns, 10 microns, or larger.

The properties of the weakly charged polyelectrolyte can be precisely controlled by changing the pH. See, eg, G. Decher, Science 1997, 277, 1232; Mendelsohn et al., Langmuir 2000, 16, 5017; Fery et al., Langmuir 2001, 17, 3779; Shiratori et al., Macromolecules 2000, 33, 4213; And US Patent Application Publication Nos. 2003/0215626 and 2007/0104922, each of which is incorporated by reference in its entirety. This type of coating can be applied to any surface treatable to the water based interlayer (LbL) adsorption process used to construct these polyelectrolyte multilayers. Since water-based processes can deposit polyelectrolytes as long as the aqueous solution contacts the surface, even the inner surface of an object with complex topography can be coated. In general, the polyelectrolyte may be applied to the surface by any method capable of treating the application of an aqueous solution to the surface, such as dipping or spraying.

Surfaces with extreme wet behavior can be prepared from polymer electrolyte coatings. See, eg, US Patent Application Publication Nos. 2006/0029808 and 2007/0104922, each of which is incorporated by reference in its entirety. The polyelectrolyte has a skeleton having a plurality of charged functional groups attached to the skeleton. The polyelectrolyte may be polycationic or polyanionic. Polycation has a backbone with a plurality of positively charged functional groups attached to the backbone, such as, for example, poly (allylamine hydrochloride). Polyanions have a backbone having a plurality of negatively charged functional groups attached to the backbone, such as, for example, sulfonated polystyrene (SPS) or poly (acrylic acid), or salts thereof. Some polyelectrolytes may lose their charge (ie, become electrically neutral) depending on conditions such as pH. Some polyelectrolytes, such as copolymers, may include both polycationic segments and polyanionic segments.

Surfaces with extreme wet behavior can be produced from multilayer films. Surfaces compliant therewith may be used, for example, in antireflective or antifog applications.

Multilayer thin films comprising nanoparticles of SiO ₂ can be prepared through interlayer assembly (Lvov, Y .; Ariga, K .; Onda, M .; Ichinose, L; Kunitake, T. Langmuir 1997, 13, (23), 6195-6203, which is incorporated by reference in its entirety). Other studies have described multilayer assemblies of TiO ₂ nanoparticles, SiO ₂ sol particles, and single or double layer nanoparticle-based antireflective coatings. For example, Zhang, XT .; Et Chem. Mater . 2005 , 17, 696; Rouse, JH; Ferguson, GSJ Am. Chem. Soc. 2003 , 125, 15529; Sennerfors, T .; Langmuir 2002 , 18, 6410; Bogdanvic, G .; Etc. J. Colloids Interface Science 2002 , 255, 44; Hattori, H. Adv. Mater. 2001 , 13, 51; Koo, HY; Etc. Adv. Mater. 2004 , 16, 21 A; And Ahn, JS; Hammond, PT; Rubner, MF; Lee, I. Colloids and Surfaces A: Physicochem. Eng. See Aspects 2005 , 259, 45, each of which is incorporated by reference in its entirety. The introduction of TiO ₂ nanoparticles into the multilayer thin film can improve the stability of the superhydrophilic state induced by photoactivation. For example, Kommireddy, DS; Et al. J. Nanosci. Nanotechnol. 2005 , 5, 1081, which is incorporated herein by reference in its entirety.

Broadband antireflection can be obtained using an inexpensive, simple process that employs an aqueous solution of the polymer. See, for example, US Patent Application Publication Nos. 2003/0215626 and 2007/0104922, which are incorporated by reference in their entirety. This process can be used to apply high efficiency conformal antireflective coatings to any shape, size, or visually any surface of material. This process can be used to apply antireflective coatings to more than one surface at a time, and to produce coatings that are substantially free of pinholes and defects that degrade coating performance. The porous polymeric material can be antireflective. This process can be used to form antireflective and anti-glare coatings on polymeric substrates. A simple and very versatile process can produce molecular-level engineered conformal thin films that function as low-cost, high-performance antireflective and anti-glare coatings. This method can homogeneously coat both sides of the substrate at once to produce a clear coating free of defects and pinholes. This process can be used to produce high-performance polymer optical components, including flat panel displays and solar cells.

Similarly, the polymer coating may be an antifog coating. The antifog coating can prevent condensation of light-scattering droplets on the surface. By preventing the formation of light-scattering droplets on the surface, the coating can help maintain optical clarity of a transparent surface, such as a lens, window or display screen. The coating can be both antireflective and antifog. The surface of the transparent objective lens with an antifog coating maintains its transparency to visible light as compared to the same objective without an antifog coating under conditions causing water condensation on the surface.

A polyelectrolyte multilayer film is used as a template to provide the surface roughness of the superhydrophobic surface. An interlayer process was used to assemble a polyelectrolyte multilayer comprising SiO ₂ nanoparticles. The film is then heated to 650 ° C. to remove the polymer electrolyte and produce the surface texture required for superhydrophobic behavior (see Soeno, T. et al. Transactions of the Materials Research Society of Japan 2003 , 28, 1207). Totally incorporated by reference). In another example, dendritic gold clusters were electrochemically deposited onto an indium tin oxide (ITO) electrode covered with a polyelectrolyte multilayer film. After deposition of the n-dodecanethiol monolayer on the gold cluster, the surface showed superhydrophobic behavior (see Zhang, X. et al. J. Am. Chem. Soc. 2004 , 126, 3064, which is incorporated by reference in its entirety). do). The electrochemical deposition process used to produce these films can define the type of material from which this method can be used to form a superhydrophobic coating thereon.

By forming a plurality of polymer electrolyte layers on the high roughness surface, a plurality of polymer electrolyte layers of high roughness may be formed. When a polymer electrolyte multilayer is formed over a high roughness surface, treatment to increase the roughness of the polymer electrolyte multilayer may be optional. High roughness surfaces include, for example, particles, such as microparticles or microspheres; Nanoparticles or nanospheres; Or a region of rising, ridges or falling. The micrometer scale particles may be, for example, clay particles or other particulate material. Rise, ridges or descent may be formed, for example, by photolithography, or by etching, positioning or otherwise depositing micrometer scale particles on a suitable substrate.

The lock-in step can prevent further changes in the structure of the pore multilayer. Lock-in can be achieved, for example, by exposure of multiple layers to chemical or thermal polymerization conditions. The polyelectrolyte may be crosslinked and cannot perform further transition to the pores. In some cases, the chemical crosslinking step may include treatment of the polyelectrolyte multiple layer with a carbodiimide reagent. Carbodiimide may promote the formation of crosslinks between amine groups and carboxylates of the polyelectrolyte. A chemical crosslinking step may be preferred when a plurality of polyelectrolyte layers are formed on the labile substrate at the temperatures required for crosslinking (such as when the substrate is polystyrene). The crosslinking step may be a photocrosslinking step. To achieve crosslinking, crosslinking can use photosensitizers (eg, photo-sensitive groups) and exposure to light (such as UV, visible or IR light). Masks may be used to form patterns of crosslinked and non-crosslinked regions on the surface. Other methods are known for crosslinking polymer chains of a plurality of polymer electrolyte layers.

Nanoparticles can be applied to multiple layers to provide nanometer-scale texture or roughness to a surface. The nanoparticles can be, for example, nanospheres such as silica nanospheres, titania nanospheres, polymer nanospheres (such as polystyrene nanospheres), or metallic nanospheres. Nanospheres can be dense or hollow. The nanoparticles can be metallic nanoparticles such as gold or silver nanoparticles. Nanoparticles can have a diameter of, for example, 1 to 1000 nanometers, 10 to 500 nanometers, 20 to 100 nanometers, or 1 to 100 nanometers. The rough, pore nature of the multilayer surface and the inherently high wettability of the silica nanoparticles establish desirable conditions for extreme wet behavior.

Superhydrophobic coatings can be produced from multiple layers without the need to treat the multiple layers to induce porosity transitions. For example, the plurality of layers may comprise a polymer electrolyte and a plurality of hydrophilic nanoparticles. See, eg, US Patent Application Publication No. 2007-0104922, which is incorporated by reference in its entirety. By selecting the appropriate assembly conditions, an adjustable thickness 3D nanopore network can be created with nanoparticles. The network may be correlated—in other words, the nanopore may form a plurality of connected voids. Rapid penetration of water into these networks (nano-wicking) can lead to superhydrophilic behavior.

Multilayer coatings comprising nanoparticles can be made with any grade of particle (and hence pore) size distribution over the coating thickness. Pore size can be measured by particle packing; The particle size and particle size distribution (polydispersity) thus greatly influence the pore and capillary size. The graded pore size distribution results in a coating having graded refractive indices over the coating thickness. In some embodiments, the coating can be functionalized; In particular the coating can be functionalized differently at different depths throughout the coating thickness. Differential functionalization can be controlled by controlling the capillary radius, which is also affected by particle size and polydispersity, and the local particle (and thus pore) size distribution in the coating, for example. Can be.

Functionalized moieties may include, for example, water, solvents, monomers such as acrylates, methacrylates, diacrylates, dimethacrylates, epoxies, urethanes, isocyanates, thiocyanates, sytrenics, and the like. Such as small molecules or PDMS, acrylate-terminated PDMS, methacrylate-terminated PDMS, diacrylate-terminated PDMS, dimethacrylate-terminated PDMS, diacrylate-terminated Polymers such as polyurethane, dimethacrylate-terminated poly (ethylene oxide) or any polymer with or without crosslinkable groups at the chain ends, and the like. The moiety may or may not be accompanied by reactive side groups. The moiety can be associated with the nanoparticle surface to form a monolayer, or thicker layer. The linkage between the moiety and the nanoparticle surface can be ionic, covalent, physisorption-based, or chemisorption-based. The coating assembly method and functionalization method may be independent and may be used separately as needed. Functionalization can be selected to result in different degrees of capillary condensation as a function of pore size and capillary radius.

Both electrostatically-mediated and reactive LbL assembly methods can be used to prepare the coating. Many different types and sizes of nanomaterials can be introduced into the interlayer assembled film. In one embodiment, polycationic poly (allylamine hydrochloride) (PAH) may be electrostatically assembled with negatively charged silica nanoparticles of size 8-50 nm. Both species can be prepared as diluted aqueous solutions, and the coating can be formed by repeated alternating dipping of the substrate in both solutions.

Graded index coatings can be made by forming a material of a first thickness on a substrate having a first refractive index. A second thickness of material, having a second refractive index, is formed over the first thickness. 1 illustrates a surface 100 that includes a substrate 110, a first thickness 120, and a second thickness 130. The first thickness 120 includes nanoparticles 140, and the second thickness 130 includes nanoparticles 150. The nanoparticles 140 may have different sizes than the nanoparticles 150. Nanoparticles of different sizes can be packed to have different void volumes. Thus, the thicknesses 120 and 130 have different effective refractive indices. Control over the refractive index in each layer is achieved by the choice of particle size, layer thickness, and particle material and functionalization.

A simulation of an optimal single-layer AR coating on a substrate (eg epoxy lens) of index ˜1.49 is shown in FIG. 4. The coating is 107 nm thick and has an index of ˜1.22, which can be achieved using LbL assembly. The extremely low refractive index in the coating is due to its high porosity, made possible by the thin packing of the nanoparticles, which leaves a substantial void volume in the coating.

With respect to FIG. 5A, there is a pressure difference across any curved interface (eg, liquid-solid interface) with finite surface tension. The pressure difference between the inside and outside of the nanoparticles is calculated by the following equation 1,

(식 1)

(Equation 1)

Where γ ^NP-L is the surface tension of the nanoparticle-liquid interface and r is the nanoparticle radius. The pressure difference across the interface increases the chemical potential in nanoparticle form compared to the chemical potential of the same material in bulk form (ie, at a flat interface), as described in Equation 2 below,

(식 2)

(Equation 2)

Where S ^NP and S ^Bulk are the solubility of the nanoparticles and bulk form of the corresponding material, respectively, Vm ^NP is the ball volume of the nanoparticle material, R is the universal gas constant and T is the temperature.

Regions (ie, pores) between neighboring nanoparticles in the coating can behave as capillaries. The liquid condensed in such pores (as shown in FIG. 5A) has a curved liquid-vapor interface and there is a pressure difference across it. This pressure difference is illustrated in Equation 3 below.

(식 3)

(Equation 3)

Where γ ^Condensate is the surface tension of the condensate-vapor interface, r _C is the capillary radius, and x is the inner diameter of the hourglass-shaped capillary condensate between the nanoparticles (see FIG. 5A). The same pressure effect of increasing the solubility of nanoparticles in solid-liquid equilibrium reduces the vapor pressure (and thus volatility) of the capillary condensate in liquid-vapor equilibrium (Equation 4),

(식 4)

(Equation 4)

Wherein P ₀ and p ₀ ^Capillary are the equilibrium vapor pressures of the corresponding liquid at flat and curved capillary liquid-vapor pressures, respectively; γ ^Condensate is the surface tension of the condensate; V _m ^Condensate is the molar volume of the condensate and x is the inner diameter of the hourglass-shaped capillary condensate between the nanoparticles.

In other words, the liquid-vapor equilibrium shifts from nanoparticle-nanoparticle capillary to liquid as compared to the flat liquid-vapor interface. Such curvature-induced condensation is called "capillary condensation".

The material has a lower vapor pressure in the capillary, so that condensation may occur in the capillary under conditions where no condensation occurs on the corresponding flat surface. The effect of capillary condensation on nanoporous films is that contaminants (including ambient water vapor) readily condense in nanopores sufficiently limited by extremely small r _Capillary . Condensation increases the refractive index of such films. Small changes in refractive index can dramatically change the optical properties. For example, when stored at 37 ° C. 80% relative humidity (rh) for 3 days, the refractive index of single layer AR film assembled LbL from 24 nm silica nanoparticles and PAH increased from ˜1.22 to ˜1.27. Subsequent changes in optical properties upon humidity aging are simulated in FIG. 4, where the top curve represents the humidity-aging sample.

Example

The low refractive index due to the pore nature of the PAH / SiO ₂ multilayer film resulted in anti-reflective properties, see, for example, US Patent Application 2007/0104922, which is incorporated by reference in its entirety. For glass substrates having a refractive index of about 1.5, when a single layer (ie no graded refractive index) antireflective coating has a refractive index of 1.22, maximum suppression of reflection loss occurs. The maximum suppression wavelength is measured by one quarter thickness of the coating. The quarter wavelength of the multilayer coating can then be tuned through the entire visible range and beyond simply controlling the number of deposited bilayers. The measurements indicate that a transmission level above 99% was achieved in the visible region (400-700 nm) (FIG. 2). For example, eight double-layer PAH / SiO ₂ 4.0 multilayer films (97 nm thick) transmitted 99.6% of incident light at a wavelength of 490 nm. Without the antireflective coating, this glass transmitted about 92% of the incident light. The ability of thin film coatings based on PAH / SiO ₂ multilayers to effectively suppress reflection loss is further illustrated by the multiple layers assembled in PAH 7.5 / SiO ₂ 9.0 (FIGS. 3A-3B). At the optimum wavelength, measured by one quarter film thickness, transmission levels of 99.7% and reflection losses as low as about 0.1% were easily achieved. The wavelength range of maximum inhibition for all of these films was much broader than expected from a single exponential one-wave antireflective coating (measured by comparison with optical simulation). This indicates that a gradient index profile has been established in the film as a result of the nano-corrugated surface topography. For example, Hiller, J .; Mendelsohn, J .; Rubner, MF Nature Mater. , 2002 , 1, 59, which are incorporated by reference in their entirety.

As shown in FIGS. 2 and 3, in the case of PAH / SiO ₂ multilayer films made from 7 nm diameter SiO ₂ nanoparticles, the thickness per bilayer deposited is a film having a quarter wavelength thickness covering the entire visible range. It was small enough to enable the manufacture of the class. This level of fine-tuning is more difficult to achieve with antireflective coatings based on a single layer of adsorbed silica nanoparticles. For example, Zhang, XT .; Et Chem. Mater. 2005 , 17, 696; Hattori, H. Adv. Mater . 2001 , 13, 51; Koo, HY; Etc. Adv. Mater . 2004 , 16, 21 A; And Ahn, JS; Colloids and Surfaces A : Physicochem. Eng. See Aspects 2005 , 259, 45, each of which is incorporated by reference in its entirety. These results also showed that coatings containing many layers of very small nanoparticles were more effective at suppressing reflections than single layer coatings made from larger nanoparticles (99.7% vs. 98.8% transmission).

The key role of any practical antifogging / antireflective coating is good mechanical durability and adhesion. The PAH / SiO ₂ multilayer film produced was well adhered and showed mechanical integrity but could be peeled off by aggressive mechanical action. The mechanical stability of these films, however, was greatly increased by heating the film to about 500 ° C. for 4 hours. This firing process burns the polymer component of the film and fuses the silica nanoparticles together through the formation of a stable siloxane bridge. For example, Unger, KK, Porous silica: its properties and use as support in column liquid chromatography . Elsevier Scientific Pub. Co .: Amsterdam; New York, 1979; See p xi, 336, which is incorporated by reference in its entirety. After this process, the resulting thin film coating can withstand aggressive rubbing treatments and can easily pass standard Scotch film peeling tests (some adhesive residues remain on the surface, but with solvent or plasma treatment Could be removed). In addition, negligible amounts of film were removed by scratching the surface with a laser blade. This process was of course only possible when the multilayer film was assembled to a substrate capable of withstanding such high processing temperatures.

The mechanical durability of nanoporous all-nanoparticles and polymer-nanoparticle interlayer (LbL) films (80-150 nm thick) was found in both glass and polycarbonate substrates through hydrothermal treatment at relatively low temperatures (124-134 ° C). (See, eg, Gemici, Z .; Shimomura, H .; Cohen, RE; Rubner, MF Langmuir 2008 , 24, 2168-2177, and US Patent Application Publication No. 2008/0038458), each of which is Totally incorporated by reference). Saturated steam may condense at the point of contact between neighboring nanoparticles. The condensed water then catalyzes neck formation at the point of contact via a dissolution-redeposition mechanism. The necking process has the same thermodynamic basis as in Ostwald ripening: nanoparticles have improved solubility (Equation 2), and dissolved species onto larger particles with sufficiently large radii of curvature. By minimizing their free energy. In nanoparticle assemblies, capillaries between neighboring nanoparticles are available, where the dissolved material deposits and forms a neck.

Poly (dimethyl siloxane) (PDMS) made of 100 nm-thick coatings of approximately various particle size distributions and saturated in a humidity chamber at 37 ° C. 80% relative humidity for 3 days, or 120 h at 100 ° C. Aged in steam or saturated tri (ethylene glycol) dimethylacrylate (TEGDMA) vapor. The percentage change in refractive index due to capillary condensation was measured (FIG. 6). Particles smaller than 50 nm induced capillary condensation much more than particles having 50 nm. Water condensation increased the refractive index to a lesser extent than PDMS condensation. Most of these effects are probably due to the higher refractive index of PDMS (n-1.46) compared to water (n-1.46), and the difference in the surface energy of silica and PDMS is due to the thermodynamic drive for PDMS condensation on the silica nanoparticle surface. You can also add In addition, the larger surface area / volume ratio of the film made by the smaller particles provides sufficient space for condensation.

LbL assembly technology enables component control as well as control of the overall thickness as a function of coating thickness. In order to obtain a multilayer structure, different coatings can be assembled on top of each other. LbL films comprising 50 nm silica particles were assembled on top of another LbL film containing 8 nm silica particles such that the overall film thickness was 90-200 nm. When this structure is exposed to PDMS or water vapor, capillary condensation occurs in both stacks, even though they have a greater impact on the refractive index of the stack made of smaller nanoparticles. Therefore, the graded particle size distribution achieved using the LbL assembly can be extended to the graded refractive index profile utilizing the thermodynamic capillary effect (FIG. 7).

Reflectance curves of such two-stack films before and after capillary condensation of water and PDMS vapor are shown in FIGS. 8A-8B. AR performance of PDMS-infiltrated graded index coatings was superior to the optimal single layer AR coating shown in FIG. 5 and was not affected by storage at 37 ° C. 80% rh for 60 hours (FIG. 9). .

PDMS condensed inside the film was retained completely at 37 ° C., but the equilibrium amount of PDMS retained is expected to decrease with increasing storage temperature. Nevertheless, once equilibrium is reached according to equation (1), the temperature-induced desorption of PDMS should stop. For example, the refractive index profile changed somewhat within the first 12 hours of storage at 85 ° C. (FIGS. 10A-10B). However, once the new equilibrium was reached, the exponential profile changed (at least in that case) to a minimum. If the temperature is lowered back to room temperature, due to the hydrophobic nature of the surface, it is expected that no more PDMS will desorb and no longer any water vapor will be adsorbed.

The overall film thickness plays an important role in measuring the position of the reflectance minimum along the x-axis (wavelength). Due to the small exponential contrast between the two stacks, the two-stack film, as assembled, behaves similarly to a single layer AR film. Thus, the reflectance minimum is located four times closer to the optical thickness. PDMS condensation improved the exponential contrast between the two stacks and shifted the reflectance minimum to a lower wavelength. Any change in the refractive index of the two stacks that reduces the index contrast shifts the reflectivity minimum to a higher wavelength, closer to its original position. For example, the two films shown in FIGS. 10A and 1OB have reflectance minimum "relax" for different thicknesses and different wavelengths when new equilibrium is reached at 85 ° C.

Reflectance spectra and refractive index profiles (blue), PDMS-functionalized (pink), and tri (ethylene glycol) dimethacrylate (TEGDMA) -functionalized (yellow) coatings as assembled are shown in FIG. 11. Is plotted on. The experimental spectrum was simulated with excellent accuracy (black curve). TEGDMA had a higher refractive index than PDMS, and this difference was observed in the refractive index of the bottom layer. Note that because the degree of capillary condensation in the top layer is negligible, the top layer was substantially the same for all three coating types.

The results of the dry heat test for PDMS- and TEGDMA-functionalized coatings, respectively, are shown in FIGS. 12A and 12B. The new equilibrium was reached within 22 hours, and some (but not all) of the condensate stable at 25 ° C. evaporated from the coating at 85 ° C. TEGDMA can be photocrosslinked by methacrylate functionality. TEGDMA-functionalized and subsequently UV-crosslinked AR coatings show essentially no change in their optical properties upon dry baking (FIG. 13).

However, since water (n-1.33) has a lower refractive index than PDMS (-1.46), the exponential contrast and hence antireflective properties are suboptimal for moisture-soaked coatings.

The organic-inorganic composite nature of the coating material can reduce mismatches between the coefficient of thermal expansion of the coating and the substrate, thereby imparting greater resistance to cracking. The thinness of the coating compared to other coatings of comparable optical performance is also advantageous in terms of avoiding cracking.

To the cleaned glass slides, 3-aminopropyl silane-modified SiO ₂ nanoparticles (15 nm diameter) and PAA polymer were deposited at pH 3.00. After depositing eight bilayers of the coating, the film was baked at 550 ° C. for 2 hours. The fired film was coated with TiO ₂ (diameter = 7 nm) and poly (vinyl sulfate) at pH 2.00. After deposition of 50 to 60 bilayers of the coating, the film was baked at 550 ° C. for 2 hours. For infiltration, calcined silica / titania stack slides were placed in vials containing PDMS (MW: 1300, n-1.46) or CH ₂ I ₂ (n = 1.74) at 100 ° C. for 20 hours. The results are shown in the table below.

The results indicated that the PDMS and CH ₂ I ₂ filled the cavity in the silica layer by penetrating through the titania layer. Relatively small amounts condensed in the titania bed cavity.

Other embodiments are within the scope of the following claims.

Claims (28)

A surface comprising a nanoporous coating comprising a first thickness having a first porosity and a second thickness having a second pore that is different from the first pore. The surface of claim 1, wherein the first thickness comprises a first plurality of nanoparticles having a first diameter. The surface of claim 2, wherein the second thickness comprises a second plurality of nanoparticles having a second diameter different from the first diameter. The surface of claim 3, wherein the coating has a thickness of less than 500 nm. The surface of claim 3, wherein the coating has a thickness of less than 300 nm. The surface of claim 3, wherein the surface is transparent. The surface of claim 1, wherein the first plurality of nanoparticles comprise a first functional moiety. The surface of claim 1, further comprising a first functionalizing compound present in the first pore as capillary condensation. The surface of claim 8, wherein the first functionalized compound is substantially free from the second pores. The surface of claim 9, further comprising a second functionalized compound present in the second pore as capillary condensation. The surface of claim 10, wherein the first and second functional compounds are different. As a coating method of the surface,
Positioning a first plurality of nanoparticles having a first diameter on the substrate; And
Positioning a second plurality of nanoparticles having a second diameter different from the first diameter on the substrate. The method of claim 12, further comprising exposing the first plurality of nanoparticles to a first functional moiety. The method of claim 13, further comprising exposing the second plurality of nanoparticles to a second functional moiety. The method of claim 14, wherein the first and second functional moieties are different. The method of claim 12, wherein the surface is transparent. As a coating method of the surface,
Positioning a first material of a first thickness having a first refractive index on the substrate;
Positioning a second material of a second thickness having a second refractive index on the substrate; And
Exposing the first material and the second material to a functional moiety. The method of claim 17, further comprising selecting a first material comprising a plurality of nanoparticles having a first size. The method of claim 18, wherein the first size is selected based on a desired first refractive index. The method of claim 18, further comprising selecting a second material comprising a plurality of nanoparticles having a second size. The method of claim 20, wherein the second size is selected based on a desired second refractive index. As a coating method of the surface,
Selecting a first plurality of nanoparticles capable of forming capillary pores having a first desired capillary radius r _C1 ;
Forming a coating on a substrate, wherein the coating comprises the first plurality of nanoparticles; And
Exposing the coating to a vapor of a functionalizing compound capable of forming capillary condensation in a capillary cavity having the first desired capillary radius r _C1 . The method of claim 22, further comprising selecting a functionalized compound capable of forming capillary condensation in the capillary cavity having the first desired capillary radius r _C1 . The method of claim 23, further comprising selecting a second plurality of nanoparticles capable of forming capillary pores having a second desired capillary radius r _C2 . 25. The method of claim 24, wherein the first plurality of nanoparticles, the second plurality of nanoparticles, and the functionalized compound are further configured to cause capillary condensation to capillary pores in which the functionalized compound has the first desired capillary radius r _C1 . Which may be formed, but is selected such that substantially no capillary condensation can be formed in the capillary void having the second desired capillary radius r _C2 . A surface comprising a nanoporous coating comprising a preselected pore and a preselected functionalized compound, wherein the functionalized compound is capillary-condensed within the pore. The surface of claim 26, wherein the nanoporous coating comprises a plurality of inorganic nanoparticles having capillary pores in the nanoparticles. The surface of claim 27, wherein the functionalized compound is a polymer or polymer precursor.

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